Electrical repeater



Feb. 20, 1934. HAFFCKE 1,947,771

ELECTRIQAL REPEATER Filed April 14, 1932 v IN V EN TOR.

P1111 IF M. fiAffC/ff.

A T TORNEY Patented Feb. 20, 1934 UNITED STATES ELECTRICAL REPEATER Philip M. Haficke, Hamden, Conn., assignor to Radio Research Laboratories Inc., a corporation of Delaware Application April 14, 1932. Serial No. 606,598

7 Claims. (01. 179-171) of the system. I attribute this improved operat- V This invention relates to circuits for electrical translating devices, particularly to circuits including gaseous conducting devices, and has for its principal object the provision of means in connection with selecting circuits for discharge devices whereby only a limited amount of the varying or alternating current component normally flowing in the grid connections will be allowed to enter the selecting or tuning circuits.

Although my present invention is useful in systems employing gas tubes of the thermionic type, it is especially applicable to systems utilizing cold cathode tubes, for instance, of the type disclosed in co-pending Heany-Haffcke application, Serial No. 548,410, filed July 2, 1931, wherein the current normally present in the grid circuit may be of the same order as that present in the anode circuit.

It will be apparent as my description proceeds that my invention differs in principle from, and is otherwise non-analogous to, grid current eliminating and/or suppressing arrangements known in the high vacuum art.

It is well known that one of the most common causes of distortion in the usual systems employing high vacuum tubes is that resulting from the presence of appreciable grid currents. My present invention is predicated upon the fact that in cold cathode tubes of the type above indicated grid current flow is a usual concomitant to normal operation. My invention has special reference to systems including tubes of the latter type and involves means whereby the normally present grid current flow is unimpeded in the tubebut issubstantially diverted from the tuning or selecting circuit connected therewith, a limited amount being allowed to pass therethrough for the purpose of regeneration control.

It may here be noted that the presence in the selecting circuits of steady potentials'other than potentials to be amplified is not always seriously detrimental in the operation of systems employing cold cathode gas tubes, but in accordance with my observations variations or fluctuations in such steady potentials may give rise to distortion and are otherwise undesirable. In carrying my invention into effect I employ in electrical association with a selector circuit, a shunt and means for controlling the intensity of variations in the current escaping the shunt which might otherwise give rise to distortion in the selector circuit.

The shunt circuit arrangement of.my invention in addition to substantially obviating distortion due to undesired currents in the input A section, serves also to increase the overall stability ing condition to the fact that the presence of the series and shunt circuits makes it possible to electrically locate the working point of the device upon the most efficient portion of the plate current-grid voltage characteristic and provides a 4 readily adjustable means for controlling the ratio between the load and the energy fed back to the input circuit. However it is understood that the invention is not limited in this respect by any theory of operation.

Other objects and features of my invention will be apparent and the invention will be more readily understood by reference to the accompanying drawing in which certain particular preferred successive stages and the couplings between such stages, the omission being in the interest of simplicity, it being understood that the invention is applicable to hook-ups having any desired number of stages.

My invention is intended for use not only in radio circuits, as shown in Fig. I, but is equally applicable to telephone and telegraph relay circuits as well as to certain industrial uses, wherein a cold cathode discharge tube is utilized as repeater and/or amplifier and/or detector.

Referring now in detail to Fig. I, an antenna, 1, is connected to a ground conductor, 2, through a coupling transformer, 3, having a primary winding, 4, and a secondary winding, 5. The terminals of secondary winding 5, which are shunted by a tuning condenser, 6, and coil, '7, are connected respectively to the electrodes 8 and 9 of a gaseous cell, 10. The cell or tube, 10, comprises an anode, 11, and a cold cathode element, 12, in addition to the input electrodes 8 and 9. A single energizing source is here simply designated by positive pole and negative pole the polarity depending to some extent upon the particular type of tube used. In the arrangement here shown the output coupling is shown symbolically at 13, and is in series with anode circuit. The output, however, may be in shunt between the anode and any one of the other electrodes, preferably the cathanode. In any event, gas in the tube affords directly and/or indirectly an internal conductive path between all of the electrodes and it is to be understood that I contemplate the use of tubes or cells of any suitable type wherein there is a conductive path between input and output electrodes, and wherein the output circuit may be in effect in shunt with the input circuit. A ballast resistor, 14, serves to limit the maximum amount of direct current permitted to pass through the tube. A

potentiometer, 15, may be included in the system' for electrically locating the working point of 10 on the proper portion of the grid voltage-plate current characteristic curve. H

The position and arrangement of coil '7 is analogous to that of the grid leak in circuits employing thermionic tubes. Its function and effect, however, are dissimilar, as will hereinafter more fully appear. Intermediate the tuning or selecting circuit 56 and coil 7 is a suppressing or blocking resistance 16, preferably although not necessarily non-inductive, which acts to limit the direct current from flowing in the selecting circuit 5-6.

As previously set forth, the grid current in circuits employing gaseous tubes may be substantially of the same order as that flowing in the anode or plate circuit; the coil '7 is preferably of high A.'C. impedance to the lowest signal frequency, but offers a path of low resistance to the direct current in the grid connections and preferably acts as a direct current shunt between grid 8 and the connections to input electrode 9. The value for resistor 14 may be determined by the current required by the tube and the voltage to be absorbed by the resistor.

The amplification constant of gas tubes is not dependent upon the geometry of the tube as in high vacuum tubes, but varies with the applied voltages, for this reason it is to be particularly understood that I. do not limit my invention to any values herein set forth, I prefer, however,

to have resistance 14 variable so that the voltages applied to the control electrode may be held within the operating limits of the device and without overloading the tube.

With the arrangement shown in Fig. I the direct current reaching tuning inductance 5 will be determined by the D. C. voltage drop across coil '7 and the resistance 16, and should be quite low, the high frequency variations or pulsations in this very small direct current flow now passing through 5 are likewise reduced to a controlled maximum enabling the tube to be maintained in a stable condition.

As indicated in Fig. II, I may utilize coil 7 as a unit of a second selecting circuit 7-,l7 in which case the value of inductance 7 is usually considerably less than that of the coil 7 of Fig. I, and should be of the order of a standard tuning unit for the frequency band to be covered. The formation of the additional tuning stage 7-17 by the insertion of variable condenser 17 materially increases the overall electivity of the assembly.

Fig. III is similar in all respects with Fig. I except that in addition to the blocking resistance 16 I may include a capacity 18 for passing high fre quency currents, the assembly 16l8 being in efiect a filter or suppressor circuit. In accordance with empiric data I find that a proper value of capacity to be of the order of .00025 and .00005 microfarads-a higher value tending to offset the desired results obtained with the resistance l6 alone.

Considered from a broad aspect, my invention covers the hereinbefore described method and means for substantially controlling the presence in, and results of, direct and/or alternating currents in a primary selecting circuit without substantially interfering with the flow of grid direct current between the input electrodes.

As a number of possible embodiments may be made of the above invention, and as changes might be made in the embodiments above set forth without departing from the spirit and scope of the invention, it is to be understood that the foregoing is to be interpreted as illustrative and not in a limiting sense except as required by the prior art and by the appended claims.

What is claimed is:

1. In an electrical system the combination of a selector circuit, a discharge tube into which said selector circuit feeds, said discharge tube having electrodes including a cold cathode, a cathanode, anode and control electrode, a filling of a conductive gas within said tube, and means for controlling the diversion from said circuit of the cathodecontrol electrode current which tends to flow therethrough.

2. An electrical system according to claim 1, in which the said selector circuit is tunable.

3. In an electrical system a selector circuit, a discharge tube having a cold cathode, a cathanode, anode and control electrode, a filling of a conductive gas within said tube and resistance means between said circuit and the grid of said tube for controlling the effects of the cathodecontrol electrode currents in said circuit.

4. An electrical system according to claim 3 in which shunt means are also provided across said cathode-control electrode for shunting from said selector circuit substantially all current variations below a predetermined frequency.

5. In combination a selector circuit, means for feeding said selector circuit with signal energy,

a two-way gaseous repeater of the cold cathode i type into which said circuit feeds, means for normally producing a current flow through said repeater independently of said signal energy, and

means for diverting substantially all said current A from said selector circuit while allowing signal to flow through said circuit due to said conductive 7 connection.

7. The combination in electrical circuits of a tunable circuit, a non-inductive impedance, an inductive impedance, a gaseous tube repeater of the cold cathode type, and circuit connections for causing said non-inductive impedance and said inductive impedance to prevent normal current flow through said repeater from flowing through said tunable circuit.

PHILIP M. HAFFCKE. 

